package com.JavaNet.net;

import java.nio.*;
import java.nio.channels.*;
import java.net.*;
import java.util.*;
import java.io.IOException;

public class EchoServer {

  public static int DEFAULT_PORT = 7;

  public static void main(String[] args) {

    int port;
    try {
      port = Integer.parseInt(args[0]);
    } catch (RuntimeException ex) {
      port = DEFAULT_PORT;
    }
    System.out.println("Listening for connections on port " + port);

    ServerSocketChannel serverChannel;
    Selector selector;
    try {
      serverChannel = ServerSocketChannel.open();
      ServerSocket ss = serverChannel.socket();
      InetSocketAddress address = new InetSocketAddress(port);
      ss.bind(address);
      serverChannel.configureBlocking(false);
      selector = Selector.open();
      serverChannel.register(selector, SelectionKey.OP_ACCEPT);
    } catch (IOException ex) {
      ex.printStackTrace();
      return;
    }

    while (true) {
      try {
        selector.select();
      } catch (IOException ex) {
        ex.printStackTrace();
        break;
      }

      Set<SelectionKey> readyKeys = selector.selectedKeys();
      Iterator<SelectionKey> iterator = readyKeys.iterator();
      while (iterator.hasNext()) {
        SelectionKey key = iterator.next();
        iterator.remove();
        try {
          if (key.isAcceptable()) {
            ServerSocketChannel server = (ServerSocketChannel) key.channel();
            SocketChannel client = server.accept();
            System.out.println("Accepted connection from " + client);
            client.configureBlocking(false);
            SelectionKey clientKey = client.register(
                selector, SelectionKey.OP_WRITE | SelectionKey.OP_READ);
            ByteBuffer buffer = ByteBuffer.allocate(100);
            clientKey.attach(buffer);
          }
          if (key.isReadable()) {
            SocketChannel client = (SocketChannel) key.channel();
            ByteBuffer output = (ByteBuffer) key.attachment();
            client.read(output);
          }
          if (key.isWritable()) {
            SocketChannel client = (SocketChannel) key.channel();
            ByteBuffer output = (ByteBuffer) key.attachment();
            output.flip();
            client.write(output);
            output.compact();
          }
        } catch (IOException ex) {
          key.cancel();
          try {
            key.channel().close();
          } catch (IOException cex) {}
        }
      }
    }
  }
}
